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Low Temperature Refrigeration Thermodynamics & Basics Main Low temperature refrigeration Thermodynamics & Basics Dr. Alexander Alekseev Linde AG, Innovation Management Main Topics • Definitions, 1st and 2nd law of thermodynamics etc. • Cooling effects • Refrigeration processes / cycles • Helium Refrigeration 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 2 1 Thermodynamics & Basics • Cooling • Heat flows from warm to cold objects • Refrigerator 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 3 Refrigerator, Definition Qo P ??? 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 4 2 Refrigerator, 1st law Conservation of energy Qo P Qamb 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 5 Interfaces Cooling capacity Qo Waste heat [capacity] Qamb Power P Qo Qamb P 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 6 3 Refrigerator / Water pump analogy 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 7 The 1st law: P + Qo = Qamb Cooling Capacity: Qo = 100 W Cooling Temperature: To = 100 K P = 100 W Waste Heat Qamb = 200 W P = 1 W Waste Heat Qamb = 101 W Is it possible? 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 8 4 Refrigerator, Carnot equation Tamb To PMIN Qo To Qo = 100 W To = 100 K Tamb = 300 K 300 K 100 K P 100W 200 W MIN 100 K 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 9 Min. power requirements (min. power consumption) Liquid Liquid Liquid Nitrogen Hydrogen Helium (LIN) (LH2) (LHe) Cooling temperature 77.4 20.1 4.2 To, K Required cooling 100 100 100 capacity Qo, W Min. power 288 1393 7043 requirements P, W P / Qo 2.9 13.9 70.4 All numbers calculated for ambient temperature Tamb = 300 K 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 10 5 Exercise An older cooling system is available with: Cooling Capacity: Qo = 300 W Cooling Temperature: To = 4.5 K Ambient Temperature: Tamb = 293 K = ca. 20 Cels Revamp: 4.5 K 1.8 K 4.5 K – refrigerator: Pmin = 300 W (293 K - 4.5 K) / 4.5 K = 19 233 W = 19.2 kW 1.8 K – refrigerator: Pmin = 300 W (293 K - 1.8 K) / 1.8 K = 45 833 W = 45.8 kW 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 11 COP – coefficient of performance COP = What you get / What you pay for What you get: Cooling capacity Qo = 300 W What you pay for: Power consumption P = 75 kW (assumpt.) Q COP o P COP = Qo / P = 0.3 kW / 75 kW = 0.004 = 0.4 % 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 12 6 Carnot efficiency (or CF, FOM) Cooling Capacity: Qo = 300 W Power Consumption: P = 75 kW COP: 0.4% According to Carnot equation: Tamb To 293K 4.2K PMIN Qo 0.3kW 19.2kW To 4.2K COPMAX Qo / PMIN 0.3kW /19.2kW 0.0156 1.6% Efficiency: e COP /COPMAX e 0.4% /1.6% 0.25 25% 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 13 COOLING EFFECTS • Joule-Thomson expansion • Expansion in turbine • Mixing of different fluids • Simon cooling • Peltier cooling • Vortex tube • etc. 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 14 7 Joule Thomson Expansion (adiabatic & isenthalpic) FlaschenventilValve Joule Thomson Effect: T 2 T T 2 T1 Temperature measurementTemperatur- 200200 bar bar meßgerät StickstoffN2 Joule-Thomson Coefficient: Ambient temperature: 300 K T Umgebungstemperatur:Ambient pressure: 1 bar T = 300 K = 27 C 1 p h const Umgebungsdruck: 1 bar 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 15 Joule Thomson expansion (adiabatic & isenthalpic) temperature - entropy diagram 11 1-2 H1 = H2 T 22 H3 = H4 3 , K , 3 3-4 T Temperature 44 17/04/2013 Fu17/04/2013ßzeile Low temperature refrigeration, Thermodynamics & BasicsSpecific entropy 16 sec 8 Joule Thomson Expansion, temperature - enthalpy diagram 1 300 NitrogenT,h - Diagramm, N2 280 300 bar 200 bar 2 260 100 bar 50 bar 240 40 bar 220 3 200 30 bar , K , 180 20 bar 10 bar 160 5 bar 1 bar Temperatur, K Temperatur, 140 120 Temperature 4 100 80 60 40 7000 9000 11000 13000 15000 17000 19000 21000 Specificspezifischeenthalpy Enthalpie,, J/mol J/mol 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 17 TURBINE 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 18 9 Expansion in a turbine 1st law: P = H1 – H2 P = 0 H1 = H2 (JT throttling) P > 0 H2 < H1 T2 < T1 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 19 Expansion in a turbine 1 300 NitrogenT,h - Diagramm, N2 280 300 bar 200 bar 260 100 bar 50 bar 240 40 bar 220 3 200 30 bar 20 bar , K , 180 10 bar 160 5 bar 2 1 bar Temperatur, K Temperatur, 140 120 Temperature 4 100 80 60 40 7000 9000 11000 13000 15000 17000 19000 21000 Specificspezifischeenthalpy Enthalpie,, J/mol J/mol 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 20 10 Expansion in a turbine, T,s-Diagramm 1 1 1-2 T D 3 3 , K , 3-4 T D 2 2 Temperature 4 1 4 p in Pideal M R Tin 1 1 pout Specific entropy 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 21 REFRIGERATION PROCESSES • Joule-Thomson - process / refrigerator • Brayton - process / refrigerator • Claude - process / refrigerator 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 22 11 Joule Heat exchanger Components: Hardware Main - Thomson process Thomson 17/04/2013 17/04/2013 Throttle valve Low temperature refrigeration, Thermodynamics & Basics & Thermodynamics refrigeration, Low temperature Basics & Thermodynamics refrigeration, Low temperature Heat exchanger Multi stage compressor Q o = H = 5 – H 1 23 24 12 Main Hardware Components: Heat Exchanger (Alu Plate Fin Heat Exchanger) Dimensions per core: up to 1.5 x 1.5 x 8.0 m Standard design temperature: -269 to +65°C (150°F) Design pressures: up to 115 bar (1640 psig) 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 25 Main Elements – Heat Exchanger Modular design allows scale up to any size 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 26 13 Main Hardware Components: Spiral Wound Heat Exchanger 17/04/2013 Fu17/04/2013ßzeile Low temperature refrigeration, Thermodynamics & Basics 27 JT - process: cool - down procedure 1 amb P 5 1 5 2b 3a 2c 3b 2 4 3 2d Heat , K , o 3c Cooling 2 object Temperature 3d 4 3 17/04/2013 Fu17/04/2013ßzeile Low temperature refrigeration, ThermodynamicsSpecific & Basics entropy 28 14 Liquefier / Refrigerator 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 29 JT- refrigerator Advantages: • Simple amb P • No moving parts in cold box reliable 1 • Produce liquid 5 Disadvantages: • High pressure compressor (100-200 bar) • Oil-free compressor [or with oil removal unit] • Relative high cost 2 4 • Relative high maintenance • Low efficiency 3 • Small-scale systems only Heat o • Cooling Temperatures above 70 K only, (theoretically above 50 K only) Cooling object 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 30 15 Open cycle JT- cooler (MMR Technologies) 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 31 Mixed gas JT-cooler based on an oil-lubricated compressor 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 32 16 Brayton-process Qo = Ptur + H5 – H1 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 33 Brayton-Verfahren 1. Cooling capacity Qo depends on - enthalpy difference at the warm end of heat exchanger (JT effect) - and expander [turbine] power: Qo = (H5 - H1) + Ptur 2. Working pressures used in a Brayton cycle are < 20 bar. The enthalpy difference (H5-H1) is therefore relative small: (H5 - H1) 0 3. Therefore the cooling capacity of the Brayton cycle is defined by the power of expander [turbine]: Qo ≈ Ptur 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 34 17 Brayton, T,s – Diagram, Nitrogen 11 5 , K , 2 Temperature 4 3 17/04/2013 Fu17/04/2013ßzeile Low temperature refrigeration, ThermodynamicsSpecific & Basics entropy 35 T,s-Diagram, Helium 10 bar 1 bar 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 36 18 T,s – Diagram, Helium 10 bar 2 4 1 bar 3 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 37 Brayton- refrigerator Advantages: • High efficiency • Pressure relative low • Low cooling temperature Disadvantages: • Cooling temperature To = var • Liquid production: very limited • Turbine • Oilfree compressor or with oil removal unit or turbocompressor • Small cooling capacity (< 500 W) difficult to realize 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 38 19 Brayton- Cooler 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 39 Claude - process Features: • Combination of an expander (turbine or piston expander) and JT valve (throttle) • intermediate pressure level (< 60 bar for nitrogen < 20 bar for helium) • gas at the outlet of expander • liquid at the outlet of JT valve 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 40 20 N2- Claude- Process, T-s-diagram 1 5 5a 2a 4a 2 3a 3 4 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 41 Claude- process Advantages . High efficiency . Compressor pressures relative low . Liquefaction possible . Therefore stable cooling temperature . Low cooling temperatures Disadvantages . Turbine . Oil-free compressor [or with oil removal unit] . Small cooling capacity difficult to realize 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 42 21 Overview, refrigerators 17/04/2013 Low temperature refrigeration, Thermodynamics & Basics 43 Helium Refrigeration • Main applications • Helium – Claude cycles • Helium Liquefier, PFD •
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